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Juncus tenuis

Willd. (1799)

This name is accepted

Kingdom: Viridiplantae Phylum: Magnoliophyta Class/Clade: Monocots Order: Poales Family: Juncaceae Genus: Juncus

bog rush, path rush, rush

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Description

Key Characters:

Growth Form: Perennial herbs.

Stems: Stems 1–6 dm long, 1–2 mm in diameter, loosely cespitose.

Roots:

Leaves: Leaves simple. Leaves basal, numerous and crowded. Blades variable in length, 7–30 cm long, 1–1.3 mm wide. Margins entire. Sheaths loose with wide hyaline margins prolonged into white scarious auricles up to 5 mm long. Stipules absent.

Flowers: Flowers (3–)numerous, borne singly on 1 side of rachis, in relatively compact dichasial cymes 1–7 cm long, forming less than ⅓ of plant, bracts 2–3, foliaceous, usually far exceeding inflorescence, each flower subtended by 2 bracteoles, these hyaline, triangular–ovate. Flowers bisexual (perfect). Perianth parts greenish, lanceolate, 3–4.5 mm long, apex long–acuminate, outer ones slightly reflexed at apex, inner ones with wide hyaline margins below. Stamens 6, ½ as long as perianth; anthers shorter than filaments. Pollen grains remaining in tetrads, surrounded by a common exine. Ovary superior, carpels 1.

Fruit: Capsules reddish brown; 1–celled; broadly ovoid; thin–walled; slightly beaked; ⅔ to rarely scarcely shorter than perianth. Seeds pale brown; oblong; 0.3–0.4 mm long; slightly apiculate at both ends.

Ploidy: 2n = 30; 32; 40; 80; 84

Habitat: naturalized in usually wet sites along trails; disturbed places; and pastures.

Elevation Range: 700–2,000 m.

Historical Distribution

Images

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Uses and Culture

USES

Natural History

Statewide Status

Naturalized

Island Status

Kaua'i Naturalized
O'ahu Naturalized
Molokai Naturalized
Maui Naturalized
Hawai'i Naturalized

Dispersal Agents


Pollinators

Bibliography

Name Published In: Sp. Pl., ed. 4, 2: 214 (1799)

Other References

Wagner et al. 1990:1454 (K, Mo, EM, H); Frohlich & Lau 2014:10 (O); Faccenda, Arthur, et al. 2025:188 (KEY); St.John 12360 BISH (Mo†, 1932)

Occurrences

SNo. Scientific Name Locality Habitat Basis of Record Description Recorded By Record Number Island Source Date
1 Juncus tenuis Halealoha Preserved_Specimen Forbes, C.N. 804 Hawaii BISH 1915-06-10
2 Juncus tenuis End of Baranaba street Preserved_Specimen Adee, K.T. Hawaii BISH 1978-03-01
3 Juncus tenuis Waikamoi Preserved_Specimen Krauss, N.L.H. 1123 Maui BISH 1967-04-15
4 Juncus tenuis Volcano House Preserved_Specimen Lee, H.A. 178 Hawaii BISH 1926-03-01
5 Juncus tenuis Growing around the foundation of the National Guard Armory, across street from Honokaa Elementary School Preserved_Specimen Herbert, W. 9777 Hawaii BISH 1996-07-03
6 Juncus tenuis Waikamoi Flume, road's end Preserved_Specimen Gagné, B.H. Maui BISH 1999-07-17
7 Juncus tenuis Along roadside Roadside Preserved_Specimen Herb to 0.4 meters. Kawelo, K. 310 Oahu BISH 2013-04-10
8 Juncus tenuis Umikoa Ranch, Hamakua c.1 acre stock pond, montane wet pasture, some koa. Preserved_Specimen As specimen Uyehara, K.J. 99092704 Hawaii BISH 1999-09-27
9 Juncus tenuis Head of Waikolu Valley, Hanalilolilo Wet rocky trail. Preserved_Specimen St.John, H. 12360 Molokai BISH 1932-12-21
10 Juncus tenuis Laupahoehoe Forest Reserve. Ca. 2 mi from Keanakolu, N Hilo District Uncommon, in wet forest of Metrosideros, Cheirodendron and ferns. Preserved_Specimen Nagata, K.M. 3896 Hawaii BISH 1988-09-25
11 Juncus tenuis Behind Pahala town to low forested hills Along cane road. Preserved_Specimen Herbst, D.R. 1769 Hawaii BISH 1970-07-13
12 Juncus tenuis Kaala bog, Mt. Kaala, Waianae Mts Occasional at parking lot. Preserved_Specimen Sedge. Nagata, K.M. 3435 Oahu BISH 1988-03-22
13 Juncus tenuis Near Puu Oo, Mauna Kea Naturalized in cattle range. Preserved_Specimen Degener, O. 20354 Hawaii BISH 1949-08-23
14 Juncus tenuis Kokee State Park, Kauai, Hawaii Growing in wet potholes in parking lot (blocked off) at base of trail to bog. Preserved_Specimen Tall dark green spikey sedge. Crago, L.M. 2005168 Kauai BISH 2005-08-03
15 Juncus tenuis Piihonua; Hilo Forest Reserve, Site 35 OS Stunted ohia wetland dieback; assoc. spp.: Metrosideros polymorpha, Myrsine sandwicensis, Vaccinium calycinum, Styphelia tameiameiae, Paspalum sp. Soil a thick peaty surface over a poorly drained ash. Substrate unkown. Water at or near the surface. Preserved_Specimen Adee, K.T. Hawaii BISH 1979-01-12
16 Juncus tenuis Hawaii National Park, Park Res. #58 Several bunches near garage. Preserved_Specimen Fagerlund, G.O. 666 Hawaii BISH 1943-07-05
17 Juncus tenuis Piihonua; Hilo Forest Reserve, Site 06 OS Stunted ohia wetland dieback; assoc. spp.: Metrosideros polymorpha (occasionally pubescent), Myrsine lessertiana, Cheirodendron trigynum, Styphelia tameiameiae & Dicranopteris sp. Soil a shallow to moderately deep poorly drained organic/ash. Preserved_Specimen Adee, K.T. Hawaii BISH
18 Juncus tenuis Umikoa, David Matsuura Property, Hamakua, Big Island, HI Growing at the edge of shallow water, along with Cyperus eragrostis, and Juncus ensifolius. Preserved_Specimen Clumping sedge, inflorescences with red tinge, taller than leaves. Crago, L.M. 2005122 Hawaii BISH 2005-03-20
19 Juncus tenuis Kilauea In pasture back of Mr. Brown's house. Preserved_Specimen Hosaka, E.Y. 1426 Kauai BISH 1936-07-06
20 Juncus tenuis Waianae Mts., Kaala Road. Roadside, wet, saturated ground. Preserved_Specimen Large number of individual clumps. Did not seem to be connected by rhizomes. Russell III, W.T. 567 Oahu BISH 2022-02-09
21 Juncus tenuis Near Puu Oo, Mauna Kea Naturalized in cattle range. Preserved_Specimen Degener, O. 20354 Hawaii BISH 1949-08-23
22 Juncus tenuis Kau District. Kilauea Forest Reserve. By IBP Study site and along the trail leading from the area Growing in open area. Preserved_Specimen Ca. 1/3 - 2/3 m. tall. Herat, T. 996 Hawaii BISH 1974-07-08
23 Juncus tenuis Olinda Pipe Line, Makawao Forest Reserve Rain forest. In water. Preserved_Specimen Herbaceous, 12 cm. height. Woolford, H.A. 123 Maui BISH 1955-12-25
24 Juncus tenuis O'ahu, Moanalua valley, about 3.5 km up valley along road above housing development. Wet, sunny area from dirt road. Preserved_Specimen Uncommon, small colony about 10 m lon seen in this area, but generally rare in the valley. Faccenda, K. 3716 Oahu BISH 2024-11-22
25 Juncus tenuis North Hilo District: Laupahoehoe, Hilo Forest Reserve Open, moist, grassy clearing. Preserved_Specimen St.John, H. 18623 Hawaii BISH 1937-12-31
26 Juncus tenuis Puu Hualalai, Puuwaawaa Opening in upper forest. Preserved_Specimen St.John, H. 11406 Hawaii BISH 1931-12-29
27 Juncus tenuis Behind Pahala, Kau District Along cane field road. Preserved_Specimen Herbst, D.R. 1769 Hawaii BISH 1970-07-13
28 Juncus tenuis Piihonua; Hilo Forest Reserve, Site 34 OS Dense healthy forest. Associated spp.: Metrosideros polymorpha (pubescent), Ilex anomala, Cheirodendron trigynum, Myrsine lessertiana, Vaccinium calycinum. Soils an extremely shallow yet well drained organic found over a pahoehoe flow. x Preserved_Specimen Adee, K.T. Hawaii BISH 1979-07-02
29 Juncus tenuis Saddle Road area, along road to Mauna Loa observatory, 1/2 mile from Puu Huluhulu Common along road. Growing with Tetramolopium, Vaccinium, and grasses near native scrub vegetation. Preserved_Specimen Leaves reddish. Davis, J. 524 Hawaii BISH 1981-06-15
30 Juncus tenuis Olinda In pastures, wet drainage. Preserved_Specimen Hobdy, R.W. 614 Maui BISH 1979-06-01
31 Juncus tenuis Kokee State Park, Kauai, Hawaii Growing in mesic to wet graded area along roadside. Preserved_Specimen Tall spikey sedge with long inflorescence, highly divided. Crago, L.M. 2005166 Kauai BISH 2005-08-03
32 Juncus tenuis Piihonua; Hilo Forest Reserve, near Site 34 OS Dense healthy forest. Associated spp.: Metrosideros polymorpha (pubescent), Ilex anomala, Cheirodendron trigynum, Myrsine lessertiana, Vaccinium calycinum. Soils an extremely shallow yet well drained organic found over a pahoehoe flow. Preserved_Specimen Adee, K.T. Hawaii BISH 1978-03-22
33 Juncus tenuis Surety Ranch LLC Stock Ponds, Kohala, Big Island, Hawaii Growing around the edges of stock ponds, in wet conditions. Preserved_Specimen Clumping sedge, inflorescences with red tinge, taller than leaves. Crago, L.M. 2005117 Hawaii BISH 2005-03-20
34 Juncus tenuis Pastures above Olinda Along an open wet gully bottom. Preserved_Specimen In dense clumps. Hobdy, R.W. 1373 Maui BISH 1982-04-30
35 Juncus tenuis Kaumalumalu, Kona District, along Jeep Trail Metrosideros, Cibotium, Cyrtandra, Psychotria, dominant with some Eurya, Pittosporum and Freycinetia. Preserved_Specimen Sohmer, S.H. 6487 Hawaii BISH 1970-07-02
36 Juncus tenuis Piihonua; Hilo Forest Reserve, wet area near Site 28 OS; Dense healthy forest. Primary vegetation: Metrosideros polymorpha (sometimes pubescent), Ilex anomala, Cheirodendron trigynum, Myrsine lessertiana, Vaccinium calycinum & Sadleria pallida. Soil a deep, moderately well drained ash. Preserved_Specimen Adee, K.T. Hawaii BISH 1979-06-21
37 Juncus tenuis Kaumalumalu, Kona District, along Jeep trail Metrosideros, Cibotium, Cyrtandra, Psychotria, dominant with some Eurya, Pittosporum and Freycinetia. Preserved_Specimen Sohmer, S.H. 6487 Hawaii BISH 1970-07-02
38 Juncus tenuis Puu Hualalai, Puuwaawaa Opening in upper forest. Preserved_Specimen St.John, H. 11406 Hawaii BISH 1931-12-29
39 Juncus tenuis Kulani Prison at end of Kulani Prison Road In disturbed soil along road. Preserved_Specimen Weed. Henrickson, J.S. 4123 Hawaii BISH 1969-08-07
40 Juncus tenuis N Hilo, Kumuula, Humuula Sheep Sta Rare, in moist ground. Preserved_Specimen Hosaka, E.Y. 2334 Hawaii BISH 1938-06-13
41 Juncus tenuis Piihonua; Hilo Forest Reserve, Site 34 OS Dense healthy forest. Associated spp.: Metrosideros polymorpha (pubescent), Ilex anomala, Cheirodendron trigynum, Myrsine lessertiana, Vaccinium calycinum. Soils an extremely shallow yet well drained organic found over a pahoehoe flow. Preserved_Specimen Adee, K.T. Hawaii BISH 1979-03-22
42 Juncus tenuis East Maui, Hana District, Haleakala Crater, Halemauu Trail, 0.3 miles before paliku cabin (on trail).road) Native shrubland area. Preserved_Specimen Lynch, E. Maui BISH 1998-07-19
43 Juncus tenuis Piihonua; Hilo Forest Reserve; Upper Wailuku River Trail Dense healthy forest. Primary vegetation: Metrosideros polymorpha (sometimes pubescent), Ilex anomala, Cheirodendron trigynum, Myrsine lessertiana, Vaccinium calycinum & Sadleria pallida. Soil a deep, moderately well drained ash. Preserved_Specimen Adee, K.T. Hawaii BISH 1979-06-21
44 Juncus tenuis Piihonua; Hilo Forest Reserve, Site 34 OS Dense healthy forest. Associated spp.: Metrosideros polymorpha (pubescent), Ilex anomala, Cheirodendron trigynum, Myrsine lessertiana, Vaccinium calycinum. Soils an extremely shallow yet well drained organic found over a pahoehoe flow. Preserved_Specimen Adee, K.T. Hawaii BISH 1979-03-22
45 Juncus tenuis Kokee, Mohihi Rd., ca. 0.1 mi past junction with Camp Sloggett Rd Preserved_Specimen The bases of some stems reddish-brown. Flynn, T.W. 1095 Kauai BISH 1985-05-10
46 Juncus tenuis Piihonua; Hilo Forest Reserve, Site 06 OS Stunted ohia wetland dieback; assoc. spp.: Metrosideros polymorpha (occasionally pubescent), Myrsine lessertiana, Cheirodendron trigynum, Styphelia tameiameiae & Dicranopteris sp. Soil a shallow to moderately deep poorly drained organic/ash. Preserved_Specimen Adee, K.T. Hawaii BISH 1979-06-11
47 Juncus tenuis Piihonua; Hilo Forest Reserve, Site 06 OS Stunted ohia wetland dieback; assoc. spp.: Metrosideros polymorpha (occasionally pubescent), Myrsine lessertiana, Cheirodendron trigynum, Styphelia tameiameiae & Dicranopteris sp. Soil a shallow to moderately deep poorly drained organic/ash Preserved_Specimen Adee, K.T. Hawaii BISH 1979-06-11
48 Juncus tenuis Keauhou Ranch, Kau District, on boundary road between Kilauea forest and Keauhou Ranch Commonly found in mud puddles. Disturbed Acacia koa - Metrosideros closed forest. Preserved_Specimen Cuddihy, L.W. Hawaii BISH 1979-12-18
49 Juncus tenuis North Kohala District; Hawi Quadrangle, Parker Ranch. Stock ponds in vicinity of Kehena Reservoir Emergent vegetation growing along shore & standing water. Floating submergent. Preserved_Specimen Engilis Jr., A. 9213 Hawaii BISH 1992-06-08
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